Comment 23 for bug 1086999

In reply to #20. dt

Ah, sorry for the confusion! I have left misleading comments from the previous version in the patch.
A universal PID controller needs to have dt inside. Because then, it is possible to deal with changing sample rates.
Lucky we have a constant sample rate during a scratch. So I have took a simplified PID controller where dt is calculated into i and d. I will put in a proper comment if we want to use D and I part one day.

One other thing is more painful: The non constant mouse sample rate, leading to bug Bug #1117806.